This should be $ReadOnly (prefix property name with +)

Can we avoid any here? Is there a flow-typed library for electron (or whatever package this is)? If not, should we introduce one?

This is the main or the "browser" thread. Whenever we detect the user navigates somewhere we send on-navigate event, which calls the callback defined in the preload.js:4 and set in the navigation-arrows.react.js.

We calls this callback with booleans that describe if user can go back and/or forward.

The preload script is used by most people for injecting variables into the renderer. And I've seen checking if the injected variables exist to determine if we are inside electron, used by a few people.

I don't think there's a way to set an env variable from the electron's main thread so that the renderer thread can see it. And if there is, we would still have to inject the variables so I don't really see a point.

The only thing the electron API is used is for determining if we can go back/ forward. As discussed in this issue it's difficult to handle this in general case.

Unfortunately not, see ENG-2221.

I've removed the event argument completely from the web callback. I don't think the code in web can do anything useful with it anyway. It also simplifies the usage.

If you think we should keep it we could type it like this:

type Event = {
  ports: MessagePort[],
  sender: IpcRenderer,
  senderId: number,
};
type IpcRenderer = {}

IpcRenderer is empty because electron doesn't pass function that are inside to the renderer thread for security reasons.

classnames returns a string so you don't need to use React.useMemo(...) here.

(Further reading: https://blog.isquaredsoftware.com/2020/05/blogged-answers-a-mostly-complete-guide-to-react-rendering-behavior/)

Good idea putting this here, thanks for thinking of that!!

Prefix with +